1. Field of the Invention
This invention relates to an image processor adapted to irradiate an original with light rays emitted from a light source and to read image information formed on the original from light rays reflected on the original and more particularly to a driving mechanism ensuring carriages to be smoothly and stably moved for scanning of the original.
2. Description of the Related Art
In the image processor of stationary original type, a light source lamp is moved relatively to an original placed on platen glass to scan the original so as to pick up image information line to line. FIG. 23 of the accompanying drawings is a perspective view schematically showing a construction of such image processor 1. In a housing 2 of the image processor 1, transversely opposite walls 2a, 2a have their inner surfaces stepped to define guide tracks 2b, 2b on which a full-rate carriage 3 and a half-rate carriage 4 are placed. These carriages 3, 4 are guided on said tracks 2b, 2b to move longitudinally of the housing 2. The housing 2 is provided on its upper surface with a platen glass (not shown) on which the original is placed. The full-rate carriage 3 carries a fluorescent lamp 5 serving as a light source lamp for irradiation of the original. A bottom plate 2c of the housing 2 is provided at its appropriate locations with an image-focusing lens 6 and photoelectric converter means 7 such as a CCD (Charge Coupled Device).
The full-rate carriage 3 additionally carries a first reflector (not shown) and the half-rate carriage 4 carries a second reflector and a third reflector (both not shown). The light rays emitted from the fluorescent lamp 5 and reflected on the original are successively reflected on said first reflector, second reflector and third reflector, then transmitted through said image focusing lens 6 and enter the photoelectric converting means 7. Via these first, second and third reflectors, and an optical path extending from the original to the photoelectric converting means 7 is established. In view of a fact that an entire area of the original must be irradiated in order to acquire the image information from the original, said full-rate carriage 3 is adapted to be movable over an entire area of the platen glass. Said optical path extending from the original to the photoelectric converting means 7 must maintain a constant length as said full-rate carriage 3 is moved. To ensure this, said half-rate carriage 4 is adapted to move in synchronization with the full-rate carriage 3 so that a movable range of said half-rate carriage 4 may substantially correspond to ½ of a movable range of said full-rate carriage 3.
FIG. 24 is a perspective view schematically showing a driving mechanism synchronously driving these carriages 3, 4. A driving shaft 8 having its axis which extends orthogonally to a scanning direction of the carriages 3, 4 is rotatably supported by the housing 2 in the vicinity of its longitudinal one end and this driving shaft 8 is provided at its longitudinally middle position with a driven pulley 9 fixed thereon. A loop of driving belt 12 is draped on said driven pulley 9 and a driving pulley 11 fixed on an output shaft of a motor 10 mounted on the bottom plate 2c of the housing 2. The driving shaft 8 is provided at each of its longitudinally opposite ends with a take-up pulley 13 fixed thereon. The drive mechanism further includes a predetermined length of wire 14 (referred to hereafter simply as “wire 14”) and an intermediate length of the wire 14 is wound around this pulley 13 by an appropriate number of turns. The half-rate carriage 4 carries on each of its end surfaces a pair of guide pulleys 15, 16 arranged side by side and being rotatable around their axes extending orthogonally to said scanning direction. Axial positions of these guide pulleys 15, 16 are different from each other so that their outer peripheral surfaces may overlap each other as will be apparent from FIG. 25. The end of the housing 2 opposed to said end provided with said drive shaft 8 carries a guide pulley 17 being rotatable around its axis extending orthogonally to said scanning direction. The sidewall 2a of the housing 2 is provided at an appropriate position with a bracket 2d. As will be obviously understood, these take-up pulley 13, wire 14, guide pulleys 15, 16, 17 and bracket 2d are pairly provided within the housing 2 so that each pair of members may be opposed to each other and define a field to be scanned therebetween.
With one end fixed to said bracket 2d, said wire 14 is draped around said guide pulley 15 positioned at a distance from the full-rate carriage 3 longer than said guide pulley 16 is, and said wire 14 is operatively associated with said full-rate carriage 3 by means 18 for this purpose. Then said wire 14 is successively draped about said guide pulley 13, said guide pulley 17 and said guide pulley 16. The other end of said wire 14 is anchored to sidewall of the housing 2 by means of a tension spring 19.
It is important that these carriages 3, 4 are smoothly movable. To meet this requirement, said carriages 3, 4 are supported on said guide tracks 2b via four legs, respectively. These legs are made of synthetic resin or the like presenting a small sliding friction relative to said guide tracks 2b made of metallic material. To assure a desired slidability of the carriages 3, 4, the contact points between said legs and said guide tracks 2b are applied with lubricant.
The photoelectric converter device 7 cannot output a desired image data unless the light rays reflected on the original reliably and stably enter the image-focusing lens 6. To achieve this, said carriages 3, 4 must be stably moved at a high accuracy. Particularly, a recent digitalization of the image processor has reduced the luminous flux width for reading the image on the original and correspondingly improved stability as well as the accuracy of the carriages' movement have been required. Said arrangement that the carriages 3, 4 are supported on said guide tracks 2b via four legs, respectively, has been developed to meet such requirement. For the conventional image processor still not digitalized, three legs have been sufficiently effective to support the carriages on the guide tracks since the luminous flux width has been relatively large.
The driving mechanism as has been described above in reference with FIG. 24 advantageously contributes to miniaturization of the image processor by arranging the half-rate carriage 4 to support said guide pulleys 15, 16 so that these guide pulleys 15, 16 overlap to each other as seen in FIG. 25 and thereby reducing a width of said half-rate carriage 4 as measured in the scanning direction. However, said wire 14 is draped on the guide pulleys 15, 16 so as to bridge these two guide pulleys and such arrangement may cause a problem will be described. In fact, said wire 14 is appropriately tensioned under a tensile force of the tension spring 19 while the half-rate carriage 4 is placed on said guide tracks 2b. Therefore, if unexpected force is exerted upon the image processor 1 during its transport or during its operation of scanning, the half-rate carriage 4 may jump up and thereupon the tensile force of said wire 14 may draw said guide pulleys 15, 16. Consequently, a new tensioned condition may be established with the half-rate carriage 4 remaining tilt and said half-rate carriage 4 cannot restore its normal position for its scanning operation. Once the half-rate carriage 4 has been retained in this jumped up position, no image data can be read from the original even if the operation of scanning is tried.
In view of the problem as has been described above, it is a first object of this invention to provide a carriage driving mechanism in the image processor improved so that, even if the half-rate carriage jumps up due to unexpected force exerted upon the image processor, said half-rate carriage is not retained in a tilted position but can restore its normal position for scanning operation.
The carriage driving mechanism of prior art has usually been accompanied with an apprehension that said lubricant applied on the leg decreases as the image processor is operated for a long period. When the lubricant decreases to a certain degree, an adequate lubricating function can be no more expected until an extraordinary noise may be generated or a smooth movement of the carriage for scanning may be obstructed. Eventually, pick-up of the accurate image data may become difficult or even impossible. In addition, once the carriage has been obstructed from its smooth movement, the carriage may readily jump up during its movement for scanning operation.
Taking account of the problem as has described just above, it is a second object of this invention to provide a carriage driving mechanism in the image processor improved so that a sufficient lubricating effect to ensure a smooth movement of the carriage is maintained even if the image processor continues to be operated for a long period.
With the arrangement that the carriage is supported on the guide tracks via four legs as has previously been described, if a precision at which said legs have been worked and/or a precision at which said legs have been mounted on the carriage is insufficient, a flatness of the carriage will be correspondingly deteriorated and the carriage will tilt. Said first-third reflectors also tilt as said carriage tilts, resulting in the reflected light rays cannot stably enter the photoelectric converter device, leading to an inaccurate image data and blurred image printed on the basis of said accurate image data. If the carriage thus tilted continues to travel along the guide track, the tensile force of said wire 14 will no more evenly act on the guide pulleys and, as a result, the carriage will readily jump up.
In view of this problem, it is a third object of this invention to provide a carriage driving mechanism in the image processor improved so that the flatness of the carriage can be adjusted to prevent said carriage from tilting even with the arrangement in which said carriage is supported on the guide tracks via four legs.